1. Field of the Invention
The present invention relates to an inkjet recording apparatus and an image forming method, and more particularly, to an image forming technology using ultraviolet-curable ink.
2. Description of the Related Art
An inkjet recording apparatus which forms a desired image on a recording medium by ejecting color ink from an inkjet head is known as a general image forming apparatus. In recent years, non-permeable (low-permeability) media, such as resin, film have been used, in addition to media having permeability, such as paper, and apparatuses which cure ink deposited on a medium by means of irradiation of ultraviolet light as active light have been proposed. An ultraviolet-curable ink used in these apparatuses contains a photoinitiator having prescribed sensitivity with respect to ultraviolet light.
In an inkjet recording apparatus which uses ultraviolet-curable ink, a light source for irradiating ultraviolet light is mounted on a carriage on which an inkjet head is installed, the ultraviolet light source is caused to be scanned so as to follow the inkjet head, and ultraviolet light is irradiated onto ink droplets immediately after landing on a medium, thereby preventing positional displacement of the ink droplets.
Japanese Patent Application Publication No. 2005-104108 discloses an inkjet recording apparatus in which a plurality of ultraviolet light sources are arranged in a direction (a nozzle arrangement direction) perpendicular to a reciprocating direction of a head, and the ultraviolet brightness distribution on the medium is made uniform, so as to prevent the occurrence of density non-uniformities. Furthermore, Japanese Patent Application Publication No. 2005-313445 discloses an inkjet recording apparatus in which an ultraviolet light irradiation apparatus is provided on either side of a recording head in a main scanning direction, and an ultraviolet light irradiation apparatus is also provided on the downstream side of a recording medium conveyance direction, in such a manner that even if ultraviolet light irradiation apparatuses of a low-output type are used, a sufficient amount of ultraviolet light for curing the ink can be obtained.
Moreover, U.S. Pat. No. 7,600,867 discloses an ultraviolet-curing type of print system in which curing light sources arranged on either side in a main scanning direction of an inkjet head are composed movably on the downstream side of the conveyance direction of the recording medium.
However, in cases where the type of medium is paper or vinyl chloride resin, or the like, and is in the form of a roll, cases where an image is formed up to the outer edges of the medium (cut sheet) (excluding cases where the image formation area is restricted to inside the medium), cases where an image is formed onto a medium of large thickness, or cases where an image is formed on a solid object (undulating surface), there is a possibility that ultraviolet light will be irradiated onto positions outside the ink deposition positions, and be reflected in unexpected directions.
FIG. 15 shows a schematic drawing of a state where image formation is carried out by ejecting ink from an inkjet head 204 onto a rigid medium 202 having a projecting surface 200. As shown in FIG. 15, ultraviolet light sources 206, 208 are provided on either side of the main scanning direction of the inkjet head 204, and when forming an image in the main scanning direction while scanning (moving) the inkjet head 204 and the ultraviolet light sources 206 and 208 along a guide 210, if ultraviolet light is radiated onto an inclined surface (edge of a projecting section) 214 on the outer edge of the image formation area 212 of the medium 202, then the ultraviolet light is radiated onto unexpected locations where the ultraviolet light is not originally supposed to be irradiated, which is undesirable from a safety viewpoint.
In FIG. 15, the direction of irradiation of the ultraviolet light is indicated by the arrow 216, and the direction of reflection of the ultraviolet light is indicated by the arrow 218; the ultraviolet light is irradiated to the outside of the image formation area 212. In the technology disclosed in Japanese Patent Application Publication No. 2005-104108, Japanese Patent Application Publication No. 2005-313445 and U.S. Pat. No. 7,600,867, it is extremely difficult to prevent irradiation of ultraviolet light onto unexpected locations in this way.